struct nlmsghdr

struct nlmsghdr {

_u32 nlmsg_len;

_u32 nlmsg_type;

_u16 nlmsg_flags;

_u32 nlmsg_seq;

_u32 nlmsg_pid;

};

 RTA_OK(rta, attrlen) returns true if rta points to a valid routing attribute; attrlen is the  running  length
       of the attribute buffer.  When not true then you must assume there are no more attributes in the message, even
       if attrlen is non-zero.
       RTA_DATA(rta) returns a pointer to the start of this attribute's data.
       RTA_PAYLOAD(rta) returns the length of this attribute's data.
       RTA_NEXT(rta, attrlen) gets the next attribute after rta.  Calling this macro will updateattrlen.  You should
       use RTA_OK to check for the validity of the returned pointer.
       RTA_LENGTH(len) returns the length which is required for len bytes of data plus the header.
       RTA_SPACE(len) returns the amount of space which will be needed in the message with lenbytes of data.